I have a similar situation whereby i need to send only two hundred emails, pause, another two hundred etc etc.

I have a daemon that sleeps every 5 mins then kicks in to see if there are any "Bulk Mails" to send.

Sleep works well for me in the daemon part where it scans for new mails every 300 seconds, and in the other part where it pauses after a run of 200 mails.

No, no spam, we've a customer base of around 300k that needs explicit communication sometimes.